Fire needs oxygen to burn, so why does it spread when we blow carbon dioxide into it?
In: Biology
Your breath still contains plenty of oxygen. Plus, it’s moving. The CO2 doesn’t really do anything once it’s made – it just sits there, not doing anything.
When a fire burns, the air next to it tends to lose its oxygen fairly quickly, meaning that the fire needs new air.
When you blow on a large enough fire, you’re adding new air to it. Sure, there’s less O2 in breath than atmosphere, but it’s still plenty for a fire.
(When you blow out something like a candle, the CO2 doesn’t really matter – it’s just that your breath is moving fast enough, to push away the hot flame and replace it with cold air. Do this enough, and the wick cools down and stops burning.)
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